The present invention is directed to a method for generating a digital alarm inhibit signal (AIS) using a pulse sequence of long strings of ones that is supplied to digital signal distributors, as well as, to an outgoing path thereof in a signal path, the pulse sequence being recognized on an incoming path and subsequently further-processed.
The periodical "telcom report", English Edition, 10 (1987) No. 5, pages 260 through 265 discloses in FIG. 8 a centrally controlled network protection switching system.
The network protection switching system reproduced in FIG. 1 contains a network management center 1, regional centers 2 through 4, digital signal distributors 5 through 12, a line terminal equipment 13, a path 15 and a backup path 16. The digital signal distributors 5 through 12 are also referred to as switching stations or as cross-connect equipment.
Path sections having, for example, repeaters and line terminal equipment that, except for the line terminal equipment 13, are not shown in the Figure are situated between the digital signal distributors 5 through 12. When an interruption 17 occurs immediately preceding the line terminal equipment 13, then the line terminal equipment 13 outputs an urgent A-Alarm at its alarm output 14 and supplies a standardized alarm inhibit signal (AIS) in the form of long strings of ones signal to the path 15 in the transmission direction. All following equipment then knows that one of the preceding equipment has already triggered an A-Alarm and has thus initiated a repair.
In the centrally controlled network protection switching system (see FIG. 1), the centers 1 through 4 are connected only to the digital signal distributors 5 through 12 and not to the intervening equipment such as, for example, the line terminal equipment 13. The regional centers 2 through 4 are informed not only of recognized AIS signals but are also informed of interruptions appearing immediately preceding the digital signal distributors 5 through 12 and of other deficiencies in the digital signal. From the line terminal equipment 13, the digital signal distributors 8 through 12 receive the same standardized AIS signal via repeaters. The regional centers 3 and 4 can now not distinguish whether only the interruption 17 is present or whether further interruptions or other deficiencies may be present between the digital signal distributors 8 and 9, 9 and 10, 10 and 11 and 11 and 12. Similarly, they cannot determine to which digital signal distributor a backup path should be optimally engaged.
European patent application EP 0 186 141 A2 discloses a digital signal distributor with which the present invention can be utilized (also see U.S. Pat. No. 4,685,101 which discloses a digital multiplexer for PCM voice channels having a cross-connect capability).
The standardized AIS signals are-forwarded onto the path either alone or in a time slot of a pulse frame of a digital signal. In the CCITT draft recommendation G.70Z, page 21, one time slot or one byte C2 is provided for this purpose in path overheads VC-4 POH, VC-31 POH and VC-32 POH in the synchronous transport module, a pulse frame of a synchronous hierarchy.